CALIBRATION OF THE RAMAN EFFECT IN ALPHA-AL2O3 CERAMIC FOR RESIDUAL-STRESS MEASUREMENTS

The pressure shifts of the 418 and 379 cm(-1) Raman lines of polycryst alline alpha-Al2O3 ceramic were measured at room temperature to 3190 M Pa. A diamond anvil high pressure cell was used in conjunction with a microRaman spectrometer system. Pressures were measured by the ruby fl uorescence method. Distilled water was used as the pressure transmitti ng medium. The pressure dependence of the wave number for the hydrosta tic range (to 1585 MPa) was found to be 0.00220 +/- 0.00007 cm(-1) MPa (-1) for the 418 cm(-1) Raman line and 0.0011 +/- 0.0001 cm(-1) MPa(-1 ) for the 379 cm(-1) line. Both shifts are based on a linear least squ ares fit to the data within a 95% confidence interval. Measurements th at included the nonhydrostatic regime (to 3190 MPa) gave similar shift s, but with almost twice the uncertainty. Absolute residual stresses i n alumina ceramics are in the 200 to 600 MPa range with higher values, 1790 MPa, reported for single-crystal alumina. For the 418 cm(-1) Ram an line, these values correspond to shifts of 0.4, 1.4, and 3.9 cm(-1) respectively. The sensitivity of the microRaman technique is sufficie nt to detect and measure residual stresses of this magnitude.